Cyclonic separating apparatus is known, for example, from EP 0 042 723 and U.S. Pat. No. 5,160,356. Both examples show domestic vacuum cleaners which operate using reverse flow cyclones to achieve particle separation. Such apparatus generally provides a cyclone body having a tangential inlet. Dirt-laden fluid flow enters the inlet and follows a helical path around the interior of the cyclone body. Centrifugal forces act on the entrained dirt to separate the dirt from the flow. The separated dirt collects at the base of the cyclone body for subsequent removal from the apparatus. The cleaned flow then changes direction and flows back up the cyclone body to exit the cyclone body via a centrally located outlet provided at the same end of the cyclone body as the inlet. Axial flow cyclonic separators can be used as an alternative to reverse flow cyclonic separators in which the cleaned flow exits the cyclone body at the same end of the cyclone body as the separated dust.
It is a known advantage to have a number of cyclones working in parallel within cyclonic separating apparatus. Each individual cyclone is small in comparison to that used in an equivalent single cyclone apparatus. The relatively small size of each individual cyclone has the effect of increasing the centrifugal force acting on particles entrained in the airflow passing through the cyclone body. This increase in the force results in an increase in the separation efficiency of the apparatus.
Cyclones can be prone to blocking. In particular, small cyclones are more likely to become blocked because there is a smaller area for the dust to pass through. Such blockages can cause a reduction in flow which has the overall effect of reducing the separation efficiency. A substantial blockage may completely stop the flow from passing through the cyclone.